Which RAID level for virtual machines in SAN

There a lot of determining factors that go into the performance feeling here. One tweak you might consider is setting up Jumbo Frames. Scott Lowe has a recent blog post here that shows some of what he did to achieve this.

You mention that the guests will be running low CPU load - those are always great candidates for virtualization - but the difference between FiberChannel and iSCSI doesn't really come into play yet.

If your vm guests are going to be running storage-intensive operations, then you have to consider that the speed of transferring a read/write operation from the VM Host to the storage array may become your bottleneck.

Since your typical iSCSI transfer rate is 1Gbps (over Ethernet), and FC is usually around 2-4Gbps (depending on how much cash you're willing to spend), then you could state that the transfer speed of FC is roughly twice as fast.

There's also the new 10Gig-E switches, but your Powervault and Powerconnect don't support that yet.

However, that doesn't really mean that the machines will work faster, as if they are running applications with low I/O, they might actually perform at the same speeds.

The debate as to which is better is never ending, and it basically will depend on your own evaluation and results.

We have multiple deployments of FC-based mini-clouds and iSCSI-based mini-clouds, and they both work pretty well. We're finding that the bottleneck is at the storage array level, not iSCSI traffic over 1Gb Ethernet.

If your core iSCSI network has been setup correctly for Equallogic you should have two separate stacks, with normal ISLs connecting the two stacks, and all arrays and hosts should have at least one connection to each stack. If that is the case then the simplest and lowest impact approach will be to follow the standard Dell firmware update procedure for stacked PowerConnects with its 2+ minute per switch timescale. You shouldn't experience any actual downtime if the cabling has been done properly but performance will be significantly degraded so you should only do this when everything is quiet. I'd be double checking that all of the connections are OK first though because you will definitely be relying on many single links keeping things alive while the upgrade happens.

Breaking out PowerConnect switches from the stack and upgrading them individually might be possible but you will have to go through a very intricate process to ensure that each switch upgrade happens in isolation and you have to be very careful reconnecting the upgraded switches because they can't be stacked until all units are at the same version. You will possibly have to recreate switch configs for most of the switches if you take this route. You will also have to ensure that all active switches have some reasonably high bandwidth connectivity to both stacks when you bring them online - that is an Equallogic requirement that seriously complicates this sort of exercise. If you end up in a scenario where one switch appears to be active as far as the arrays are concerned but is isolated from either stack then at best you will have some serious performance problems and at worst all volumes hosted from the arrays connected to that switch may go offline. I really wouldn't want to do it that way to be honest, far too many points at which it could go wrong.